This invention relates to a sheet and a blade for shaping a sheet folding portion, and more particularly a sheet foldable along a folding portion, and a blade for shaping the folding portion on the sheet, which are applicable, for example to manufacturing of a clear case ( a box formed by folding a plastic sheet).
There have been known sheets adapted to be folded, such as one described in the Japanese Unexamined Utility Model Application Publication No. Sho-63-91455. The sheet described in the cited publication includes a recessed groove disposed orthogonal to a sheet folding direction, and a folding portion including recesses and protrusions formed on the bottom portion of the recessed groove in the lengthwise direction (Prior Art 1).
Unlike the recesses and protrusions, it is also known the sheet with holes intermittently formed on the bottom portion of the recessed groove in the lengthwise direction thereof (Japanese Unexamined Patent Application Publication No. Sho-64-40317, Prior Art 2).
The sheets of the Prior Arts 1 and 2 each are foldable precisely along the recessed groove, and possess capabilities of maintaining the strength and preventing the breakage of the sheet through shallow portions of the recessed groove, while exhibiting foldability through deep portions or intermittently formed holes of the recessed groove, thereby rendering the sheet foldable.
As a sheet described in the Unexamined Japanese Patent Application Publication No. Hei-1-150520, it is also know a sheet with reinforcing ribs shaped between the recesses and protrusions on the bottom portion of the recessed-groove in the lengthwise direction (Prior Art 3).
However, any conventional sheets as described above pose problems that they have the folding portion of less strength when a deeply recessed groove is provided or the protrusions in the recessed groove are shaped with smaller dimension, and on the contrary, they have less foldability when the protrusions are shaped with larger dimension in order to maintain the strength of the sheet.
That is, taking the Prior Art 3 for example, the reinforcing ribs are shaped perpendicular to the recessed groove (in the folding direction), so that the reinforcing ribs abut against each other when the sheet is folded towards the side thereof with the recessed groove, thereby preventing the sheet from folding. This poses a problem of deteriorating the foldability of the sheet. In addition, the sheet with the smaller reinforcing ribs shaped for assuring the foldability also poses a problem of lacking the sheet strength.
On the other hand, when the sheet is folded towards the side thereof without the recessed groove, the reinforcing ribs are subjected to the force applied in the sheet tearing direction, so that the reinforcing ribs may be broken or similar events may occur. When the larger reinforcing ribs are shaped to prevent such a breakage, it also poses a problem of deteriorating the foldability of the sheet.
The present invention has been conceived to solve the above problems. It is an object of the present invention to provide a sheet that is capable of simultaneously satisfying the demands on the foldability and the strength of the sheet.
The present invention has been conceived to solve the above problems by providing a sheet, which includes a sheet body 10 such as a plastic sheet with a folding portion 12 provided perpendicular to the folding direction X, which is characterized by that the folding portion 12 includes a large number of recesses 14 and remnants 16 between the recesses 14 shaped on the sheet body 10, boundary lines 18 defined between the recesses 14 and the remnants 16 each are tilted at acute angle with respect to the folding portion-forming direction Y and towards the same side as that of an opposing one of the boundary lines 18 with a corresponding remnant 16 therebetween.
According to the sheet of the present invention having the above arrangement, when the sheet body 10 is folded along the folding portion 12 in the folding direction X, the remnants 16 each having the corresponding opposite boundary lines 18 tilted towards the same side are brought into a twisted state, so that the remnants 16 are unlikely to abut each other. In addition, even if the force is effected on the remnants 16 in the sheet tearing direction, the tilted boundary lines 18 of the remnants 16 can disperse the tearing direction oriented force, thereby preventing the breakage of the remnants 16.
Thus, the sheet of the above arrangement is advantageous in the fact that it can simultaneously satisfy the demands on the foldability and the sheet strength.
According to the sheet of the present invention, all the boundary lines 18 between the recesses 14 and the remnants 16 are preferably tilted in such a manner as to be aligned parallel to each other. This advantageously enables the folding portion 12 to be easily shaped.
The boundary lines 18 between the recesses 14 and the remnants 16 each are preferably tilted at an angle of 5 degrees or more with respect to the folding portion-forming direction Y, which advantageously enables the folding portion 12 to be easily shaped. That is, if the tilting angle is less than 5 degrees, the shaping of the folding portion 12 of the sheet body 10 involves a troublesome work. In addition, when the folding portion 12 is shaped such as by the pressure effected by a blade for shaping the sheet folding portion, the blade may decrease the strength of its own. To solve these problems, the tilting angle is more preferably set to 10 degrees or more.
On the other hand, the tilting angle is preferably set to 60 degrees or less, thereby enabling the sheet to sufficiently exhibit its strength. That is, when the tilting angle is set to more than 60 degrees, it is unlikely to smoothly disperse the tearing direction oriented force caused on the remnants 16, with the result that the breakage of the remnants 16 cannot reliably be prevented. To reliably prevent such a breakage, the tilting angle is more preferably set to 30 degrees or less.
Each recess 14 has the length L1 in the folding portion-forming direction Y, which is preferably set to 0.5 times or more the sheet thickness H. When the folding portion 12 with the tilting angle of less than 0.5 times is shaped by the blade, the blade is unlikely to assure a sufficient strength. As a result, the blade may have a nicked edge during the mass production of the sheet. On the contrary, the tilting angle of 0.5 times or more renders the sheet suitable for the mass production.
The length L1 of each recess 14 in the folding portion-forming direction Y is preferably set to 100 times or less the sheet thickness H. When the folding portion with the recesses 14 each having the length L1 of 100 times or more is applied to an assembly case or the like, corner portions thereof are largely deformed, posing problems that the assembly case cannot be firmly assembled, and hence the folding portion may be broken. On the contrary, the length L1 of 100 times or less is advantageous that the folding portion 12 is prevented from being broken.
Further, each remnant 16 has the length L2 in the folding portion-forming direction Y, which is preferably set to 0.3 times or more the sheet thickness H. When the length L2 of the remnant 16 is set to less than 0.3 times, the strength is extremely reduced, with the result that the sheet may be torn apart at the folding portion 12. On the contrary, the length L2 of 0.3 times or more is advantageous that the sheet is prevented from being torn apart at the folding portion 12.
Still further, the length L2 of each remnant 16 in the folding portion-forming direction Y is preferably set to three times or less the sheet thickness H. The remnants 16 each having the length L2 set to more than three times tend to harden, allowing the folding portion 12 to be easily broken. On the contrary, the length L2 of 3 times or less is advantageous that the sheet is prevented from being broken at the folding portion 12.
It is possible to adjust the magnitudes of the foldability and the strength of the sheet by varying the tilting angle of the boundary lines 18 with respect to the folding portion-forming direction Y, the length L1 of the recesses 14 in the folding portion-forming direction Y, the length L2 of the remnants 16 in the folding portion-forming direction Y, the depth of the recesses 14, the thickness of the remnants 16, or the like. The numerical values as mentioned above are thus determined according to the thickness and material of the sheet, as well as the intended use of the sheet.
According to the present invention, there is also provided a blade for shaping the sheet folding portion 12 including the recesses 14 and the remnants 16 shaped on the sheet body 10 such as a plastic sheet, which is characterized by that a blade body 20 includes a plurality of protrusions 24 for shaping the recesses 14 and cut-outs 26 each shaped between the protrusions 24, and the cut-outs 26 each have opposite side walls 28 which are tilted towards the same side and at acute angle with respect to the folding portion-forming direction Y.
When the blade of the present invention having the above arrangement is applied to the shaping of the folding portion 12 on the sheet body 10 such as a plastic sheet, it is possible to shape the recesses 14 between the remnants 16 by means of the protrusions 24, while leaving the portions corresponding to the cut-outs 26 intact. In this regard, the cut-outs 26 each have the opposite side walls 28 tilted towards the same side and at acute angle with respect to the folding portion-forming direction Y, so that the folding portion 12 can be shaped on the sheet body 10 with the recesses 14 and the remnants 16 defining the boundary lines 18 each tilted at acute angle with respect to the folding portion-forming direction Y and towards the same side as that of an opposite one of the boundary lines 18 with a corresponding remnant 16 therebetween.